1. Field of the Invention
The present invention relates generally to the field of three-dimensional (3-D) displays. More specifically, the invention relates to a system and methods for true 3-D display suitable for multiple viewers without use of glasses or tracking of viewer position, where each of the viewers' eyes sees a slightly different scene (stereopsis), and where the scene viewed by each eye changes as the eye changes position (parallax).
2. Related Art
Over the last 100 years, significant efforts have gone into developing three-dimensional (3-D) displays. To date none of these efforts have been truly satisfactory. There are existing 3-D display technologies, including DMD (digital-mirror-device, Texas Instruments) projection of illumination on a spinning disk in the interior of a globe1 (Actuality Systems); another volumetric display consisting of multiple LCD scattering panels that are alternately made clear or scattering to image a 3-D volume2 (LightSpace/Vizta3D); stereoscopic systems requiring the user to wear goggles (“Crystal Eyes” and others); two-plane stereoscopic systems (actually dual 2D displays with parallax barrier, e.g. Sharp Actius RD3D); and lenticular stereoscopic arrays3 (many tiny lenses pointing in different directions, e.g., Phillips nine-angle display, SID, Spring 2005). Most of these systems are not particularly successful at producing a true 3-D perspective at the users eye or else are inconvenient to use, as evidenced by the fact that the reader probably won't find one in her/his office. The Sharp notebook only provides two views (left eye and right eye, with a single angle for each eye), and the LightSpace display appears to produce very nice images, but in a limited volume (all located inside the monitor,) and would be very cumbersome to use as a projection display.
Beyond these technologies there are efforts in both Britain and Japan to produce a true holographic display. Holography was invented in the late 1940s by Gabor4 and started to flourish with the invention of the laser and off-axis holography5,6. The British work is farthest along11, and has actually produced a display that has a ˜7 cm extent and an 8 degree field of view (FOV). While this is impressive, it requires 100 million pixels (Mpixels) to produce this 7 cm field in monochrome and, due to the laws of physics, displays far more data than the human eye can resolve from working viewing distances. A working 50 cm (20 inch) color holographic display with a 60-degree FOV would require 500 nanometer (nm) pixels (at least after optical demagnification, if not physically) and more than a Terapixel (1,000 billion pixels) display. These numbers are totally unworkable anytime in the near future, and even going to horizontal parallax only (HPO, or three-dimensional in the horizontal plane only) just brings the requirement down to 3 Gpixels (3 billion pixels.) Even 3 Gpixels per frame is still a very unworkable number and provides an order of magnitude more data than the human eye requires in this display size at normal working distances. Typical high-resolution displays have 250-micron pixels—a holographic display with 500 nm pixels would be a factor of 500 more dense than this—clearly far more data would be contained in a holographic display than the human eye needs or can even make use of at normal viewing distances. Much of this incredible data density in a true holographic display would just go to waste.
FIG. 1 shows a present generation volumetric 3-D display. The technology is amazing, but a spinning object enclosed in a glass bowl is a poor candidate for interactive technologies, immersive technologies, or remote collaboration since it gives no chance of being involved in the scene. It also has the even more difficult problem of all objects in the display being transparent.
Another form of volumetric 3-D display has been proposed by Balogh12, 13, 14, 15 and developed by Holografika. This system does not create an image on the viewing screen, but rather projects beams of light from the viewing screen to form images by intersecting the beams at a pixel point in space (either real—beams crossing between the screen and viewer, or virtual—beams apparently crossing behind the screen as seen by the viewer). Resolution of this type of device is greatly limited by the divergence of the beams leaving the screen, and the required resolution (pixel size and total number of pixels) starts to become very high for significant viewing volumes.
Eichenlaub16 teaches a method for generating multiple autostereoscopic (3-D without glasses) viewing zones (typically eight are mentioned) using a high-speed light valve and beam-steering apparatus. This system does not have the continuously varying viewing zones desirable for a true 3-D display, and has a large amount of very complicated optics. Neither does it teach how to place the optics in multiple horizontal lines (separated by small vertical angles) so that continuously variable autostereoscopic viewing is achieved. It also has the disadvantage of generating all images from a single light valve (thus requiring the very complicated optical systems), which cannot achieve the bandwidth required for continuously variable viewing zones.
Nakamuna, et al.17, have proposed an array of micro-LCD displays with projection optics, small apertures, and a giant Fresnel lens. The apertures segregate the image directions and the giant Fresnel lens focuses the images on a vertical diffuser screen. This system has a number of problems including: 1) extremely poor use of light (most of the light is thrown away due to the apertures); 2) exceedingly expensive optics and lots of them, or alternatively very poor image quality; 3) very expensive electronics for providing the 2-D array of micro-LCD displays.